src/newusers.c: A user/group name with a leading digit is valid

[alejandro-colomar]

Only consider a string to be a UID/GID if it is all digits.

Closes: #1474

---

Revisions:

v1b

• Add reproducer to commit message.

$ git rd 
1:  f26af1fee ! 1:  497cbf1fe src/newusers.c: A user/group name with a leading digit is valid
    @@ Commit message
     
         Only consider a string to be a UID/GID if it is all digits.
     
    +    Here's a reproducer of the bug:
    +
    +            $ echo 'foo:p::1a::/tmp/nonexistent:/usr/bin/false' > x
    +            $ sudo newusers ./x
    +            newusers: invalid group ID '1a'
    +            newusers: line 1: can't create group
    +
    +    Where the expected behavior would be the same as for a group name that
    +    doesn't start with a digit:
    +
    +            $ echo 'foo:p::a1a::/tmp/nonexistent:/usr/bin/false' > x
    +            $ sudo newusers ./x
    +            $ tail -n1 /etc/group
    +            a1a:x:1004:
    +            $ tail -n1 /etc/passwd
    +            foo:x:1004:1004::/tmp/nonexistent:/usr/bin/false
    +
         Closes: <https://github.com/shadow-maint/shadow/issues/1474>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>